Question

An elevator is descending with uniform acceleration. A person in the elevator drops a

marble at the moment the elevator starts to measure the acceleration of the elevator.

The marble is 2 m above the floor when it is dropped. It takes 1.2 s to reach the floor

of the elevator. What is the acceleration of the floor. Take g = 10 ms-2

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Answer 1

Explanation:

For elevator and coin u=0

As the elevator descends downward with acceleration a′ ( say)

The coin has to move more distance than 1.8 m to strike the floor. 

Time taken t=1 sec

sc=ut+21a′t2=0+1/2g(1)2=1/2 g

se=ut+21at2=u+1/2g(1)2=1/2 a

Total distance covered by coin is given by =1.8+1/2a=1/2g

⇒1.8+a/2=9.8/2=4.9

⇒a=6.2 m/s2=6.2×3.28=20.34 ft/s2.